Self-regulating emission control by a high leakage type transformer



Oct. 22, 1968 W. C. HICKMAN SELF-REGULATING EMISSION CONTROL BY A HIGH LEAKAGE TYPE TRANSFORMER Filed Feb.

Fig.2

NO LOAD FULL LOAD L INVENTOR. WALLACE C. HICKMAN AGET Unifgd States Patent: F

ABSTRACT OF THE DISCLOSURE A high leakage reactance 'transfornie'ris provided with a primarywinding', ta highvoltage secondary wjinding, and athird windingmagnetically' coupled tothe second winding for supplying filament volt age sin an electron discharge device; Because of the significantly, high leakage r'eactanc of the transfor'nier t'hedoad current; supplied by the high voltage secondary winding affects th'e ivolt age output of the third WindingQTliuS the filament or he'ater voltage in a high "voltageleleetron discharge 'deviceis v v I Background of the invention I: (1) Field of 'the invention-This invention'relates" to a direct function of the load "currentflowing, through the power supplies and more par'ticularlyto an automatic filament voltage controlling system for'athermionically operable vacuum tube.

(2) Description of the prior art-In thermionically operable electron discharge devicesemploying high voltage anodes and-electron emissives filaments or cathodes,

it isoften desirable to control the cathode heater. current in accordance with the magniture of the-anode. current being drawn. In certain types of electron emissive devices such as conventional vacuum tubesit may be desirable to provide increasing filament voltages with increasing magnitudes of anode current being drawn. In othertypes of devices, such as the magnetron, the life characteristic of the cathode. is deleteriously;affected;v by: overheating, an effect directly related to back bombardment of the cathode by the electrons-under high anode" current load conditions. The latter situation optimumly requires that the cathode temperature be held constant under increased load situations.

Efforts to control the cathode heater current in accordance with the device load current has resulted in elaborate arrangements utilizing relays, servo systems, manual potentiometers, and other similar and expensive types of control system-s. One proposed alternative to the foregoing has been to provide a cathode assembly structure of two dissimilar metals having varying thermal coefficients of expansions. By suitable placement of contacts, expansion and contraction of the thermal elements control the application of voltage to the heater, thereby maintaining the cathode within a safe operational temperature range. However, the principal disadvantage of the foregoing arrangement is the necessity of having to construct a bimetallic heater element as an integral portion of any tube in which it is necessary to control the cathode heater current.

It is therefore a prime object of this invention to provide a circuit arrangement which will regulate the electron emissivity of any thermionically operable electron discharge device. It is a further object of this invention to provide an automatic control system for varying cathode heater current in accordance with the degree of anode current in an electron discharge device.

It is another object of this invention to reduce the harmful effects of high operating cathode temperatures in magnetron tubes by reducing cathode heater current under conditions of increasing anode current.

3,407,333 P atented Oct. 22, I968 Summary of the invention invention utilizes aileakage reactance. transformer having a primary winding, a secondary high voltage winding and athird winding magnetically coupled to the secondary high voltage winding and having sutficient turns to provide suitable heater current for an electron discharge device of either the. conventional or the magnetron variety. The ,leakage. reactance transformer hasthe property of allowing anadded voltage build-up. across the filament supply .winding in, proportion to the magnitude of current, flowing in the high voltage windingBy Properly are rangingthe filament voltage winding, i ncreases in current flowingthrough the high voltage winding can have the elfect of either raising or lowering thevoltage appear ingacrossthe filament winding; In this manner, filament voltage control becomes a factor directly dependent upon the ,degree or magnitude of current'fiowing, through the high voltage winding.

- Brief description of the drawings FIG. 1 is a schematic illustration of a conventional electron discharge device provided with a stand-by filament voltage in accordance with this invention; FIG. 2 is-another embodiment of the invention schematically illustrating amagnetron being provided with automatically controllable filament voltage in accordance with the present invention; FIG. 3 schematically illustrates the voltage relationships of the arrangement of FIG. 2.

Description of the preferred embodiments Referring to FIG. 1 there is shown a transformer core constructed of a suitable magnetic material and having a plurality of magnetic flux paths defined by transformer legs 12, 13 and 14. The transformer leg 12 includes a nonmagnetic series gap 15 which represents a relatively high leakage reactance path with respect to legs 13 and 14 and requires a relatively high magnetizing force to approach saturation or to highly magnetize the gap. The" transformer leg'14 includes a primary winding'16 coupled to a source of alternating current power 17. Transformer leg 13 includes a secondary high voltage winding 18 and a further secondary winding 19 having a number of turns in relation to the primary windings sufficient to supply proper filament voltage to an electron discharge device illustrated as a conventional vacuum tube 20. The high voltage secondary winding 18 is coupled through a capacitor 21, a rectifier 22, and a load resistance 23 to the anode 24 of the discharge device 20. The further secondary winding 19 is coupled to a filament 25, while a cathode 26 is coupled to the other polarity terminal of the rectifier 22. In operation, because of the relatively high magnetizing force required to saturate the transformer core 10, an increasing load current drawn through the output load terminal 27 of the electron discharge device 20 will result in increased current through the secondary winding 18. The resulting increased magnetic flux flowing through the transformer legs of secondary winding 18 and the magnetically coupled winding 19 will result in an increased voltage appearing at the output of the second ary winding 19. Decreasing load currents will have the opposite effect.

The arrangement of FIG. 1 is designed to be self regulatory with regard to variations in supply voltage. The leakage reactance of the transformer 10 and the reactance of the capacitor 21 are chosen to be theoretically equal in impedance magnitude at a frequency above line frequency. At line frequency, the effective impedance of the secondary circuit will exhibit a capacitive rather than inductive characteristic. If the supply voltage should vary, for example to a higher value than is designated, an increasing current begins to fiow into the transformer priachieved and current flow stabilized.

fiRefe'rring to -FlGi-2,'--'a similar a'rrangein'erit to that disclosedfor FIG. lis described-in connection with controlling' the filamentvolta'ge' applied to a 'rnag'ri'etron28. In'this arrangement transformer core '29 is provided with an additional'filament voltage-control winding--30 which crease. n. magn lictfiux auses.

is--connect'eil in s eries with'a conventional filament voltage co'ntro'l Winding- 31. Windings 30*and'31 have been placed on the core 29in-inagnetieally OppositesensesJAs shown in 'FIG. 2-, E represents the voltage output fromthe wind; ing 30;- Eg, represents the voltage outputtrorri' the winding 31, and E 'represe'nts the algebraic suni'of the'voltages" E andE as ap'plied' tothe'filament of themag 'net'r'on 28. Referring now toFIG."3', under no load conditions, winding E will provide a voltage ofa fir's't' magnitude and winding E a voltage of second and opposite magnitude, resulting in a third voltage E representing the algebraic difference between. the voltages E and E being applied to the filament of the magnetron. As the load increases (lower half of FIG. 3) current flowing through the secondary high voltage winding 32 of the transformer core 29' of FIG. 2 will'increase, thereby increasing the voltage E produced at the output of winding 31. The resultant voltage E is' thereby decreased. In this manner an automatic mode of operation results in decreasing the filament voltage applied to a magnetron with increases of load current through the magnetron, thereby eliminating the deleterious effects of overheatlng.

I Although'several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined' by the appended claim.

"I claim; V

1. In combination with a loadable electron discharge device having no load to full loadoperating current conditions and includinga high voltage electrode and a thermionically emissive element, an automatic voltage tregulationsystem for adjustingthevoltage appliedtto said thermionically emissive element inversely with the change in load current flow magnitude to said high voltage electrode, comprising, a transformer core having a plurality of legs, one Qf said legs i'ncluding a nonmagnetic gaptor inipart'ing- "gnifi'cantf. leakage ,rea'ctance' characteristic tq saidj core afirst iwinding coupling a.fiist leg of said tiransfojrmelrl core toasource of alt er nating line current power, a' second winding coupled-to a second leg of said transformerfcore; a.third Winding having a first half coupled to saidfirst--legand a'second half coupled to said second leg, said first and second halves series coupled in voltage opposi'ri'g sense's',said'third winding coupled to said thermionically emissive element for supplying voltage thereto, a capacitor having a reactive impeda'iic'e substantially equal to the reactive impedance of said core' leakag'e r'eactance'ht a frequency above the'freque'ncy fof 'saizl' line current source,='m'e ai1s connecting saidcapajcitorbfetweenf said second winding and said high voltage electrode, "said'cap'acitor and said leakage're- 'actahc'e' forming a first total'irilpedance at no load and aseco'ndtotal" impedance at' fulll6ad,f said second total impedance being greater'in magnitude than said first total References Cited 1 UNITED STATES PATENTS 11/1934 Kirsten 315106 X 2,001,567 5/1935 Case 315-406 2,048,203' 7/1936 Spencer .i. 315-106 2,236,195 v 3/1941 McKesson L 315-106 -2;504,548 4/1950 "Lemmers 315-106 I Rohloff et al. 31s 1f0 7 X JAMES w. LAWRENCE, Primary Examiner. c, R. CAMPBELL, 4mm: Exanririer. 

